diff options
Diffstat (limited to 'src/ref/lilliput-i.c')
| -rw-r--r-- | src/ref/lilliput-i.c | 67 |
1 files changed, 38 insertions, 29 deletions
diff --git a/src/ref/lilliput-i.c b/src/ref/lilliput-i.c index 6f869c3..fb06237 100644 --- a/src/ref/lilliput-i.c +++ b/src/ref/lilliput-i.c @@ -32,58 +32,67 @@ static const uint8_t _0n[BLOCK_BYTES] = { }; +static uint8_t _upper_nibble(uint8_t i) +{ + return i >> 4; +} + +static uint8_t _lower_nibble(uint8_t i) +{ + return i & 0x0f; +} + static void _init_msg_tweak(const uint8_t N[NONCE_BYTES], uint8_t tweak[TWEAK_BYTES]) { /* With an s-bit block index, the t-bit tweak is filled as follows: * - * - bits [ 1, t-|N|-4]: block index - * [ 1, s]: actual block index - * [ s+1, t-|N|-4]: 0-padding - * - bits [t-|N|-3, t-4]: nonce - * - bits [ t-3, t]: 4-bit prefix + * [ 1, 4]: 4-bit prefix + * [ 5, |N|+4]: nonce + * [ |N|+5, t]: block index + * [|N|+5, t-s]: 0-padding + * [t-s+1, t]: actual block index, from MSB to LSB * - * This function sets bits s+1 to t-4 once and for all. + * This function sets bits 5 to t-s once and for all. */ - size_t N_start = TWEAK_BYTES - NONCE_BYTES - 1; - - for (size_t i=sizeof(size_t); i<N_start; i++) - { - tweak[i] = 0; - } - - tweak[N_start] = lower_nibble(N[0]) << 4; + tweak[0] = _upper_nibble(N[0]); for (size_t i=1; i<NONCE_BYTES; i++) { - tweak[N_start+i] = lower_nibble(N[i]) << 4 ^ upper_nibble(N[i-1]); + tweak[i] = _lower_nibble(N[i-1]) << 4 ^ _upper_nibble(N[i]); } - tweak[TWEAK_BYTES-1] = upper_nibble(N[NONCE_BYTES-1]); + tweak[NONCE_BYTES] = _lower_nibble(N[NONCE_BYTES-1]) << 4; + + /* The number of bits we need to zero out is: + * t - |N| - s - 4 - 4 + * (prefix) (zeroed out by previous assignment) + */ + memset(&tweak[NONCE_BYTES+1], 0, TWEAK_BYTES-NONCE_BYTES-sizeof(size_t)-1); } static void _fill_msg_tweak( - uint8_t prefix, - size_t block_index, - uint8_t tweak[TWEAK_BYTES] + uint8_t prefix, + size_t block_index, + uint8_t tweak[TWEAK_BYTES] ) { /* With an s-bit block index, the t-bit tweak is filled as follows: * - * - bits [ 1, t-|N|-4]: block index - * [ 1, s]: actual block index - * [ s+1, t-|N|-4]: 0-padding - * - bits [t-|N|-3, t-4]: nonce - * - bits [ t-3, t]: 4-bit prefix + * [ 1, 4]: 4-bit prefix + * [ 5, |N|+4]: nonce + * [ |N|+5, t]: block index + * [|N|+5, t-s]: 0-padding + * [t-s+1, t]: actual block index, from MSB to LSB * - * This function assumes bits s+1 to t-3 have already been set, - * and only sets bits 1 to s and t-3 to t. + * This function assumes bits 5 to t-s have already been set, and + * only sets bits 1 to 4 and t-s+1 to t. */ - copy_block_index(block_index, tweak); + uint8_t *msb = &tweak[0]; + *msb = prefix<<4 ^ _lower_nibble(*msb); - uint8_t *msb = &tweak[TWEAK_BYTES-1]; - *msb = prefix<<4 ^ lower_nibble(*msb); + copy_block_index(block_index, tweak); } static void _encrypt_message( |